Method and apparatus to delay deterioration of brake oil

ABSTRACT

A method and apparatus for controlling the liquidity of brake actuation liquid and to delay deterioration of its original properties by means of operating one or more, opening and closing elements in response to actuation and release of the brake pedal at an appropriate place adjacent to a liquid pressure cylinder of a liquid pressure brake which brakes a rotating part of a wheel, and forcing the brake actuation liquid having been heated in said liquid pressure cylinder to flow back to a storage tank through a discharging part of the opening and closing element immediately when the fluid pressure induced into the liquid pressure cylinder is released.

United States Patent Hayama 1 Sept. 12, 1972 [54] METHOD AND APPARATUS TO DELAY DETERIORATION OF BRAKE OIL [72] Inventor: Akio I-Iayama, No. 1/7 Miyakojima- Hondori-S-chome, Miyakojima-ku, Osaka, Japan [22] Filed: Nov. 23, 1970 [2]] Appl. No.: 91,752

FOREIGN PATENTS OR APPLICATIONS Germany ..l88l264 D Primary Examiner-Evon C. Blunk Assistant Examiner-Douglas D. Watts Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT A method and apparatus for controlling the liquidity of brake actuation liquid and to delay deterioration of its original properties by means of operating one or more, opening and closing elements in response to actuation and release of the brake pedal at an appropriate place adjacent to a liquid pressure cylinder of a liquid pressure brake which brakes a rotating part of a wheel, and forcing the brake actuation liquid having been heated in said liquid pressure cylinder to flow back to a storage tank through a discharging part of the opening and closing element immediately when the fluid pressure induced into the liquid pressure cylinder is released.

10 Claims, 14 Drawing Figures PATENTEDSEP 12 I972 SHEET 1 IF 4 AKIO HAYANA,

INVENTOR ATTORNEYS PATENTEU I973 3.690.422

SHEET 2 BF 4 AKIO PLAYAMA,

I NVENT OR.

BYAJMAAmA ZZUM AKIO HAYNIA,

INVENTOR BYMMM 4M ATTORNEYS INVENTOR. Malawi $644414;

AKIO HAYAMA,

ATTORNEYS PATENTEDsEP 12 m2 sum u BF 4 i A .WL/aA we, an

METHOD AND APPARATUS TO DELAY DETERIORATION OF BRAKE OIL The present invention is related to a method apparatus which makes it possible to automatically remove air having come into the liquid pressure pipe in a fluid system to brake wheels of an airplane or a motorcar, to adjust liquidity of the brake actuation liquid, to maintain stability of the liquid against local heat conduction, and to delay deterioration of its properties.

In these days of super-highways being expanding widely, the braking effect at the time of stopping a motorcar is becoming a matter of increasing importance. Safer brake controlling systems, lining, brake actuation liquid, etc. are main problems to consider. Above all, the speed-up of motorcars demands that the brake actuation liquid (hereinafter called the actuation liquid) have the ability to stand against far severer conditions.

Usually, many of the known actuation liquids are made of a mixture of glycolic alcohol and an appropriate amount of a stabilizer, anti-oxidant, anti-corrosive agent, etc. Besides, there are many propositions to physically improve the activation liquid as well as its additives aiming at such a product that is more stabilized at high temperature and that does not lose liquidity and yet maintains long-service quality.

Generally, in the case of repeated sudden stops of a train or a motorcar which is running at a high speed, local heating of a disk lining is conducted to the pressurized fluid through a piston, a cylinder, etc., due to which even an actuation liquid of the highest quality comes immediately to the boiling point and its braking power drops.

As a matter of fact, the actuation liquid is stored in a storage tank and is distributed to a master cylinder a liquid pressure pipe individual liquid pressure cylinders. When a brake pedal is depressed, the distributed actuation liquid moves slightly under the influence of the fluid pressure produced by the master cylinder. While, when the brake pedal is released, the actuation liquid returns almost to its original position and stays there. Accordingly, the liquid lacks liquidity in the cold season and comes to have local deterioration remarkably under the influence of the heat produced on the wheels, due to which there arises such a defect as it is difficult to obtain proper braking at the time of sudden braking action.

Besides, in the case of air having come into the liquid pressure pipe, it cannot be removed unless an air discharging valve provided adjacent to each liquid pressure cylinder is opened and several operators work separately on the side of the liquid pressure cylinder and on the side of the brake pedal. But, such operation lacks accuracy. If and when there is any stagnation of a mass of air, suitable braking effect cannot be obtained since air is more easily compressed than the actuation liquid.

Accordingly, in view of the fact that a vehicle equipped with a drum brake adopts such a circulation system that, when the brake pedal is depressed, the actuation liquid having been pressed into each wheel cylinder via the liquid pressure pipe is successively restored to the storing tank via the returning pipe, the objects of the present invention are to make it possible to maintain the liquidity of the actuation liquid, to maintain its original viscosity by means of pushing the actuation liquid having been heated at the wheel cylinder which have been greatly affected by friction heat of a tire toward the returning pipe so as to reduce its temperature to an appropriate level, and thus to maintain a normally required braking efficiency by means of delaying the speed of its deterioration as much as possible.

Further, in various kinds of disk brakes used to brake the wheels of a motorcar or an airplane and also to brake the rotating elements of various kinds of machines, another object of the present invention is, when the brake pedal is released (or when the brake lever pulled by hand is returned to its original position), to make it possible to maintain the liquidity of the ac-. tuation liquid which has been pressed into each liquid pressure cylinder via the liquid pressure pipe by means of, restoring the liquid successively to the storage tank from the returning pipe via the discharging part of the opening and closing element which collaborates with the action of the fluid pressure, to maintain the required braking effect by means of adjusting the temperature of the actuation liquid having been heated in the liquid pressure cylinder which has been greatly affected by the friction heat of a tire to an adequate temperature by an appropriately provided cooling device, and to thus delay its deterioration as much as possible.

Further, when there is indication of air having come into either the liquid pressure cylinder or the liquid pressure pipe, another object of the present invention is to offer a method which facilitates maintenance of the required braking effect by means of stopping the vehicle and repeating the stopping action on the brake pedal just a few times and thus discharging the air through the outlet of the returning pipe.

The abovementioned objects and advantages of the present invention will be explained further in detail in the following with reference to the attached drawings.

The invention will now be described with particular reference to the accompanying drawing, wherein:

FIG. 1 is an illustration of an embodiment of the present invention carried out on a vehicle;

FIG. 2 is a view with a partial cut-off to show another embodiment of the present invention carried out on a drum brake;

FIG. 3 is a partial sectional view to show another embodiment of the present invention carried out on caliper-type disk brake;

FIG. 4 is a partial side view taken along lines 1-] in FIG. 3;

FIG. 5 is a partially magnified view of a part of FIG. 3;

' FIG. 6 is a similar view to FIG. 3 and shows the position of a simplified movable valve element;

FIG. 7 is a partially magnified view of the main part of an opening and closing element to be actuated by fluid pressure of another system;

FIG. 8 is a view to show the normal position of the opening and closing element of a further different fluid pressure system, which is equipped with a rack and a pinion engaging with each other on lines falling at right angles;

FIG. 8a is a sectional view taken along lines IIIIIIII, in Fig. 8;

FIG. 9 is a plan view of 'a rotary plate with a shaft I hole and which is rotatable by pressurized fluid;

FIG. 10 is a sectional view taken along lines II-II in FIG. 11 and shows an opening and closing element equipped with said rotary plate;

FIG. 11 is a view taken along lines III-III in FIG. 10, in which a partical cut-off has been made to the depth of lines III-III in order to show the rotary plate, a returning spring, a controller and a partially open state of an outlet hole;

FIG. 12 is a partial sectional view of an opening and closing element, in which a ball is set on the top of a piston rod which is to be actuated by an electromagnetic coil and a smaller-diameter part of said piston rod forms a passage for the actuation liquid; and

FIG. 13 is a view taken along the arrows in FIG. 12.

In FIG. 1 and FIG. 2, a valve cylinder 3 is provided adjacent to a wheel cylinder 2 of a drum system 1, and has therein a seal element 5 around mounted a moving valve element 7 having inlet holes 6, 6A for pressurized fluid and a spring 4 for biasing the valve element. Between the wheel cylinder 2 and the valve cylinder 3 an inlet hole 68 and a return hole 8 are provided. An induction channel 9 into cylinder 3 is connected with a master cylinder 13 via a liquid pressure pipe 10 and, a return pipe 12 connects a return hole 8A into cylinder 3 with a tank 11. When a brake pedal is depressed, the fluid pressure produced by the master cylinder 13 is conducted to the valve cylinder 3 via the liquid pressure pipe 10. The moving valve element 7 moves to the right, against the pressure of spring 4 and, after closing the return hole 8, opens communication between the inlet holes 6A, 6B. Then, the conducted fluid pressure pushes pistons 14 provided in the wheel cylinder 2 to the right and left. Brake shoes 15 are expanded with anchor pins (which are not shown in the drawing) as a fulcrum and contact brake drums 16 fixed to wheels. The friction thus produced brakes the rotation of the drum 16 and the wheels stop turning. When the brake pedal is released, the fluid pressure is released and the spring 4 pushes back the moving valve element 7 to its original position and, after closing the inlet holes 6A, 63, opens communication between the return holes 8, 8A. Additionally, the actuation liquid in the wheel cylinder 2 which has been heated is caused by the contracting movement of a returning spring of the brake shoe 15, to be restored to the storage tank 11 through the return holes 8, 8A and the return pipe 12. Further, taking the summer heat into consideration, it may possible to adjust the temperature of the actuation liquid to an adequate level by means of providing a heat radiating device 17 with fins at an appropriate part of the return pipe 12. (Hereinafter, for facilitating distinguishment of a part in one drawing from a similar part in other drawings, different marks will be used in each drawing) FIG. 3 shows an embodiment of the present invention in a disk brake, in which a U-shaped yoke 21 has a closed end on the side spaced from the disk 22 and an open end on the side adjacent to the disk 22.- Liquid pressure cylinders 24 are formed in the yoke to align parallel to the axis of a wheel shaft 23, and sliding pistons 25 are sealed in those cylinders by O-shaped rings 26. As most clearly seen in FIG. 5, each liquid cylinder 24 has on one side an inlet hole 27 and an outlet hole 28, bath intersecting a valve cylinder 29. The valve cylinder 29 has on one side a closed end and on the other side a connection 30 for joining with the liquid pressure pipe 10. Further, a movable valve element 32 with inlet holes 27A, 278 at one end and seal element 31 at the other end is inserted into the cylinder.

FIG. 5 shows that the movable valve element 32 has been moved from the position indicated with a dotted line to the solid line position by the fluid pressure when the brake pedal is depressed. In the process of such movement, valve element 32 first closes the outlet hole 28, thus securing the sealing of the inside of the liquid pressure cylinder 24 and then communication of the fluid pressure to cylinder 24 is open through inlet holes 27A, 27B and 27. When the brake pedal is released, the fluid pressure is released and a spring 33 pushes up the movable valve element 32. In this process, the inlet hole 278 is first closed and the outlet hole 28 is opened and the piston 25 which is returning by a piston spring (which is not shown in the drawing) forces the heated actuation liquid from the outlet hole 28 to the return pipe 12 and further to the storage tank 1 1. Usually, the liquid pressure cylinder is situated at a lower position than the master cylinder, due to which some amount of the actuation liquid remains and there is no fear of causing hindrance on braking effect.

An embodiment shown in FIG. 6 resembles that of FIG. 5 closely, but is characterized by a simplified movable valve element 32A. Valve element 32 is mere ly cylindrical, without inlet openings therein, but is dimensioned such that when the brake pedal is depressed, valve element moves downwardly to below inlet 27 to allow fluid into cylinder 24. When the pedal is depressed the movable valve element 32A is urged upwardly by spring 33 and in accordance with the back movement of the piston 25 the heated actuation liquid flows to the return pipe 12 through the outlet hole 28.

An embodiment shown in FIG. 7 is another suitable example to attain the object of the present invention. On one side of the liquid pressure cylinder 24 a swinging element 35 is hinged onto a supporting rod 34. Between the cylinder 24 and a connection 30A for communication with the liquid pressure pipe 10, a valve cylinder 38 is provided and has then a valve element 37 with inlet holes 36, 36A. In parallel with the valve cylinder 38, another valve cylinder 38A is provided between the cylinder 24 and a connection 30B for communication with the return pipe 12 and has therein a valve element 37A. These valve elements 37, 37A are respectively sealed in the valve cylinders 38, 38A together with controlling springs 40, 40A by stopping rings 42,which have therein small holes 41 communicating with cylinder 24. One end of each valve element contacts a respective end of the swinging element 35.

This drawing shows the state of operation of all the parts of the opening and closing element at ordinary times, i.e. when the brake pedal is not depressed. When the pedal is depressed, the pressurized fluid flows to the inlet hole 36 through the liquid pressure pipe, whereby the valve element 37 moves to the right and the swinging element 35 pushes the valve element 37A to the left to a position shown by the dotted line, thus closing an outlet hole 39A and opening the inlet hole 36A. Accordingly, the pressurized fluid pressed into the sealed liquid pressure cylinder 24 pushes the piston 25 toward a disk 22. When the brake pedal is released, the fluid pressure is released instantly and the controlling spring 40 pushes the actuating element 37 quickly to its original position, closing the inlet hole 36A. Simultaneously, the actuating element 37A is pushed by the controlling spring 40 to the position shown in the drawing, whereby the actuation liquid induced into the liquid pressure cylinder which has been overheated under the influence of friction heat of the tire is forced into the return pipe.

An embodiment shown in FIG. 8, too, can attain the object of the present invention. Between an opening 45 connected with the liquid pressure pipe and the liquid pressure cylinder 24, a valve cylinder 48 is provided and has therein a slider valve 47 with a rack 46 and inlet holes 45A, 45B therein. The slider valve 47 is sealed together with a return spring 49 by a stopper 50 with a small hole 41A therein. A cylinder 52 is provided in such way that it intersects both a discharge path 51 connected with the return pipe 12 and the abovementioned valve cylinder 48, and has therein a rotating element 54 equipped with a pinion 53 on one end engaging rack 46 and an outlet hole 51A on the other end.

FIG. 8 shows the state of operation of all the parts of the opening and closing element at ordinary times, i.e. when the brake pedal is not depressed. When the pedal is depressed, the pressurized fluid flowing in through the opening 45 pushes the slider valve 47 to the right and the rack 46 turns the engaged rotating element 54 about 90 degrees, thus closing the outlet hole 51A, and then opens the inlet hole 458 and allows the pressurized fluid into the liquid pressure cylinder, whereby the piston 25 is pushed toward the disk 22. When the pedal is released, the fluid pressure is released and the return spring 49 pushes back the slider valve 47 to its original position thus closing the inlet hole 45B. At almost the same time, the rack 46 turns the engaged rotating element 54 in the reverse direction about 90 degrees and opens the outlet hole 51A, whereby the actuation liquid heated in the liquid pressure cylinder which has been overheated under theinfluence of friction heat of the tire is pushed through the discharge path 51 by the'piston 25 which is returning to its original position and is successively restored to the storage tank 11.

Besides the aforementioned embodiments, it is also possible to carry out the back flow of the heated actuation liquid by means of rotary plate 61 with a shaft hole 60, as shown in FIGS 9-11 as an opening. and closing element. That is to say, when the brake pedal is depressed, the pressurized flowing from the liquid pressure pipe 103 fills an actuation liquid chamber 62, as shown in FIG. 11, and acts on a pressure-receiving surface 61A of the rotary plate 61. The rotary plate 61 turns against a return spring 64, closing an outlet hole 63 and, after securing the sealing of the inside of the liquid pressure cylinder 24, opens an inlet hole 65. Thereby, the pressurized liquid is induced into the liquid pressure cylinder and a lining fixed on the piston 25 presses the disk 22. When the pedal is released, the fluid pressure is released and the rotary plate 61 is returned by the return spring 64, thus closing the inlet hole 65 and opening the outlet hole 63 and returning to its original position for gearing with a controlling element 67. Thereby, the heated actuation liquid is pushed toward the returning pipe 123 by the back pressure of the piston 25 and is successively restored to the storage tank in accordance with the operation of the brake pedal.

Further, the object of the present invention can also be easily attained by means of a valve together with a ball or other desires of a like nature as an opening and closing element. As shown in FIG. 12 & FIG. 13, a diamagnetic sleeve 77 for a piston rod 71 which is actuated by magnetic force of an electromagnetic coil fixed on one side of the liquid pressure cylinder 24, a smaller-diameter part 71A provided on said piston rod 71, and a ball 72 form a ball valve 72A, which controls an inlet hole 73 and an outlet hole 74. To explain this embodiment further, a lead 75 is connected with either a control light circuit fixed to the brake pedal or an exclusive circuit (which is not shown in the drawing). When the brake pedal is depressed, the control light is lighted by the electric current from a secondary battery. At the same time, the piston rod 71 which had closed the inlet hole 73 due to the pressure of a spring 76 is moved downwardly by the magnetic action of the electromagnetic coil 70, and, the smaller-diameter part 71A is isolated from outlet hole 74, thus closing outlet hole 74 and opening the ball valve 72A. Thereby, the

pressurized fluid coming through a liquid pressure pipe 10c pushes the piston 25 toward the disk 22. When the pedal is released, the circuit of the electromagnetic coil 70 is switched off and the spring 76 pushes the piston rod 71 back to its original position, closing the ball valve 72A and opening the outlet hole 74. Thereby, the heated actuation liquid is pushed toward a return pipe by the back pressure of the piston 25 and is successively restored to the storage tank.

The aforementioned embodiments are mainly designed to eliminate stagnation of the actuation liquid by the physical circulation method, to avoid local deterioration of the actuation liquid under the influence of friction heat of the tire, to make it possible to extend the usable running distance of the brake actuation liquid, to remove any air which may have entered the liquid pressure cylinder and emit it into the open air automatically during the repetition of ordinary operation of the brake pedal. However, the aforementioned embodiments are regarded as more examples to explain the present invention in detail and do not give any strict limitation to the application of the present invention.

Accordingly, it is a matter of course that certain change in design and form should be permitted when carrying out the present invention.

Whatl claim is:

1. A method for cooling brake actuation liquid to prevent deterioration thereof for use in a vehicle brake system including a master cylinder operable by a brake pedal; a plurality of individual wheel liquid pressure cylinders, each having braking means movable therein; a plurality of valve cylinders, each positioned adjacent one of said liquid pressure cylinders; an inlet hole communicating each valve cylinder with its respective liquid pressure cylinder; an outlet hole communicating each liquid pressure cylinder with is respective valve cylinder; a valve element movably positioned in each of said valve cylinders; a liquid storage tank; a plurality of liquid pressure pipes connecting each of said inlet holes with said master cylinder; and a plurality of return pipes connecting each of said outlet holes with said storage tank;

said method comprising the steps of:

depressing said brake pedal to force pressurized liquid through said liquid pressure pipes to act on each of said valve elements;

causing said pressurized liquid to move said valve elements from inoperative positions to operative positions to close said outlet holes, while substantially simultaneously opening said inlet holes, thereby forcing said liquid into said liquid pressure cylinders to force said braking means into a braking position;

thereafter releasing said brake pedal to interrupt the flow of said liquid from said master cylinder through said liquid pressure pipes;

causing said valve elements to return from said operative positions to said inoperative positions; thus closing said inlet holes while substantially simultaneously opening said outlet holes; and forcing said liquid in said liquid pressure cylinders through said return pipes toward said storage tank;

whereby said liquid which is in heat conductive relationship with said braking means is periodically circulated away therefrom upon selective depression and release of said brake pedal.

2. A vehicle brake system comprising: a master cylinder operable by a brake pedal; a plurality of individual wheel liquid pressure cylinders, each having braking means movable therein; a plurality of valve cylinders, each positioned adjacent one of said liquid pressure cylinders; an inlet hole communicating each valve cylinder with its respective liquid pressure cylinder; an outlet hole communicating each liquid pressure cylinder with its respective valve cylinder; a

valve element movably positioned in each of said valve cylinders and having means for selective blocking one of said inlet hole or outlet hole while unblocking the other of said inlet hole or outlet hole and means for urging said valve element into said blocking position; a

connecting each of said inlet holes with master cylinder; and a plurality of return pipes connecting each of said outlet holes with said storage tank.

3. A system as claimed in claim 2, wherein said braking means comprise pistons operable to force brake shoes against a rotating brake drum; said valve element comprises a piston movable in said valve cylinder and having inlet openings selectively communicable between said liquid pressure pipe and said inlet hole.

4. A system as claimed in claim 2, wherein said braking means comprise pistons operable to force brake pads against a rotating brake disc.

5. A system as claimed in claim 4 wherein said valve element comprises a piston movable in said valve cylinder and having inlet openings selectively comm unicable between said liquid pressure pipe and said inlet hole.

6. A system as claimed in claim 4, wherein said valve element comprises a piston movable in said valve cylinder and dimensioned to block said outlet hole while unblocking said inlet hole and to block said inlet ho e while unbloc i sa' outl th le.

. A system as c ziir ne in claim 2, wherein said valve element comprises a first piston selectively blocking said inlet hole; a second piston selectively blocking said outlet hole; and a swinging element engaged by both said first and second pistons.

8. A system as claimed in claim 4, wherein said valve element comprises a slider valve having a rack thereon; and a rotating element having a pinion thereon engaging said rack, said rotating element further having an outlet opening selectively communicable with said outlet hole.

9. A system as claimed in claim 4, wherein said valve element comprises a rotary plate swingable within said valve cylinder.

10. A system as claimed in claim 4, wherein said 7 valve element comprises a piston rod; and electromag- P0-105U UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3690422 Dated September 12, 1972 Inventor(s) AKIO HAYAMA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the Patent, after line 7, insert Foreign Application Priority Data November 25, 1969 Japan.. ..94549/69 Signed and sealed this 13th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHT.R,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A method for cooling brake actuation liquid to prevent deterioration thereof for use in a vehicle brake system including a master cylinder operable by a brake pedal; a plurality of individual wheel liquid pressure cylinders, each having braking means movable therein; a plurality of valve cylinders, each positioned adjacent one of said liquid pressure cylinders; an inlet hole communicating each valve cylinder with its respective liquid pressure cylinder; an outlet hole communicating each liquid pressure cylinder with is respective valve cylinder; a valve element movably positioned in each of said valve cylinders; a liquid storage tank; a plurality of liquid pressure pipes connecting each of said inlet holes with said master cylinder; and a plurality of return pipes connecting each of said outlet holes with said storage tank; said method comprising the steps of: depressing said brake pedal to force pressurized liquid through said liquid pressure pipes to act on each of said valve elements; causing said pressurized liquid to move said valve elements from inoperative positions to operative positions to close said outlet holes, while substantially simultaneously opening said inlet holes, thereby forcing said liquid into said liquid pressure cylinders to force said braking means into a braking position; thereafter releasing said brake pedal to interrupt the flow of said liquid from said master cylinder through said liquid pressure pipes; causing said valve elements to return from said operative positions to said inoperative positions; thus closing said inlet holes while substantially simultaneously opening said outlet holes; and forcing said liquid in said liquid pressure cylinders through said return pipes toward said storage tank; whereby said liquid which is in heat conductive relationship with said braking means is periodically circulated away therefrom upon selective depression and release of said brake pedal.
 2. A vehicle brake system comprising: a master cylinder operable by a brake pedal; a plurality of individual wheel liquid pressure cylinders, each having braking means movable therein; a plurality of valve cylinders, each positioned adjacent one of said liquid pressure cylinders; an inlet hole communicating each valve cylinder with its respective liquid pressure cylinder; an outlet hole communicating each liquid pressure cylinder with its respective valve cylinder; a valve element movably positioned in each of said valve cylinders and having means for selective blocking one of said inlet hole or outlet hole while unblocking the other of said inlet hole or outlet hole and means for urging said valve element into said blocking position; a liquid storage tank; a plurality of liquid pressure pipes connecting each of said inlet holes with master cylinder; and a plurality of return pipes connecting each of said outlet holes with said storage tank.
 3. A system as claimed in claim 2, wherein said braking means comprise pistons operable to force brake shoes against a rotating brake drum; said valve element comprises a piston movable in said valve cylinder and having inlet openings selectively communicable between said liquid pressure pipe and said inlet hole.
 4. A system as Claimed in claim 2, wherein said braking means comprise pistons operable to force brake pads against a rotating brake disc.
 5. A system as claimed in claim 4 wherein said valve element comprises a piston movable in said valve cylinder and having inlet openings selectively communicable between said liquid pressure pipe and said inlet hole.
 6. A system as claimed in claim 4, wherein said valve element comprises a piston movable in said valve cylinder and dimensioned to block said outlet hole while unblocking said inlet hole and to block said inlet hole while unblocking said outlet hole.
 7. A system as claimed in claim 4, wherein said valve element comprises a first piston selectively blocking said inlet hole; a second piston selectively blocking said outlet hole; and a swinging element engaged by both said first and second pistons.
 8. A system as claimed in claim 4, wherein said valve element comprises a slider valve having a rack thereon; and a rotating element having a pinion thereon engaging said rack, said rotating element further having an outlet opening selectively communicable with said outlet hole.
 9. A system as claimed in claim 4, wherein said valve element comprises a rotary plate swingable within said valve cylinder.
 10. A system as claimed in claim 4, wherein said valve element comprises a piston rod; and electromagnetic coil means to selectively move said rod downwardly in said valve cylinder. 